[PATCH] remove needless check in fs/read_write.c

nr_segs is unsigned long and thus cannot be negative.  We checked against 0
few lines before.

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>